It is 6.30 on Monday morning at Heathrow. In the Star Centre, a windowless central operations room lined with banks of screens showing Heathrow’s many chokepoints, the first of three daily telephone conferences is taking place – this one to anticipate glitches in a day that will see about 210,000 passengers, 1,300 flights and 50,000 vehicles arrive or depart from the world’s busiest international airport.

The Terminal 1 service manager reports a heavy flow of passengers as businessmen fly off at the start of the week. The engineers report that two jetties for arriving planes are out of action. The baggage manager says 300 bags that have missed connecting flights are lying in a reclaim hall. Somebody else says that several jumbos full of passengers with onward flights will be arriving close together, so every security lane in the Flight Connections Centre must be open. The disembodied voice of Greg Ward, the operations director, then praises everyone for a “fantastic” weekend’s work and urges them to ignore the protest camp against Heathrow expansion that has appeared on the airport’s northern fringe.

“Keep focusing on the everyday operation,” Ward implores them, “because it’s going to be the best summer we’ve had.” I catch my breath. “The best summer we’ve had”? To most observers, it has been Heathrow’s summer from hell. Almost daily a politician or business leader has labelled Heathrow a national disgrace that is damaging Britain’s stature and competitiveness. Passenger surveys have voted it one of the world’s worst airports. Newspapers have been full of travellers’ horror stories. The Competition Commission is investigating whether to break up BAA’s monopoly ownership of Heathrow, Gatwick and Stansted after a litany of complaints from airlines.

The phrase “Heathrow hassle” has entered the lexicon, and commentators have vied to produce the most colourful put-downs – a “really expensive mall with planes”, “customer service reminiscent of the worst days of nationalised British Rail”, scenes “reminiscent of Nairobi slums”. Heathrow has also been described as an airport “bursting at the seams” and “held together by sticking plaster” – and that came from Tony Douglas before he resigned as BAA’s chief executive last month.

BAA – owner of this little-loved gateway to Britain – has become an even juicier target since it was taken over by the Spanish company Ferrovial last year, so in an attempt to defend itself it agreed to let The Times spend a day behind the scenes.

What I find during 13 bewildering hours spent rushing along Heathrow’s labyrinthine corridors, down into cavernous basements and through countless security checks, is indeed a wretchedly outdated airport. But I also learn a little about the murky world of aviation politics and the conflicting agendas of its major players. And I develop a grudging sympathy for BAA, caught between the public’s ever greater demand for (hassle-free) air travel on one side and – on the other – an increasingly powerful environmental lobby and ever stricter security regulations.

The Times photographer and I join Ward, a burly 34-year-old former Ford production manager, for breakfast in an office plastered with performance charts and a sign that declares “Delivering Operational Excellence”. He explains that the Star Centre receives reports from each terminal every 15 minutes, and that he receives text messages on the length of Heathrow’s queues every hour of every day, even on holiday.

He believes in “measurements”, not “perceptions”, and what his measurements tell him – despite all the anecdotal evidence to the contrary – is that 91 per cent of Heathrow’s passengers waited less than 10 minutes to get through security in July, and that figure has not dropped below 95 per cent in August. In the past year he has opened 13 more security lanes, making 68 in total, and employed 600 more security officers, making 2,500 in all. He still needs 250 more security officers but that takes time, he insists, arguing that he needs 10,000 applicants to find 300 good recruits.

I am sceptical, but the only long security queue we find as we tour the terminals is in the Flight Connections Centre (FCC), temporarily overwhelmed by the almost simultaneous arrival of two large jumbo jets. Short security queues do not automatically mean happy passengers, however. There are the usual snaking lines in front of the British Airways check-in counters, for which BAA has no responsibility. There is also an embarrassingly long line of at least 200 disgruntled overseas passengers waiting in the FCC while just four immigration officers check their passports. Eight other counters are unmanned. Again, BAA says it can only request – not demand – more immigration officers.

BAA also argues, with justification, that it is not responsible for restricting passengers to one piece of hand luggage containing no liquids, gels or sharp objects – another source of intense irritation. Ward claims that despite all the publicity more than half Heathrow’s passengers still arrive with prohibited items, and nearly a quarter ignore the compliance officers who advise passengers what they can and cannot take on board before they reach the scanning machines.

In Terminal 4 we watch an Asian man desperately trying to squash his wheeled-suit-case into the size-checker, and breaking its handle as he tries to yank it out again. Bradley Wilkins, a compliance officer, politely sends him back to his airline counter to check it in. Wilkins, who is just 16, reckons that about 5 per cent of passengers respond angrily when he stops them. One told him he was “about as much fun as a pork pie at a Jewish party”. A couple of times a day he will have to summon a supervisor.

Carol King, a security officer who trains colleagues to do body searches, said a few passengers even object to being frisked, though most eventually comply. She has never found anything suspicious – just objects deliberately planted on people to test the searchers. She says that criticism of Heathrow’s security checks is “totally unfair. Our job is to keep people safe, and we do it to the best of our ability”. Sometimes the worst thing about searching passengers is their personal hygiene – “You are up close and personal with everybody and it’s not always pleasant.”

In the Terminal 1 reclaim areas we find the pile of 300 bags sitting unattended in a corner. Richard Wazacz, BAA’s 33-year-old head of logistic operations, admits that Heathrow’s baggage-handling record is “unacceptable” but – unsurprisingly – he insists that the airlines are to blame.

Wazacz takes us into a control room lined with screens showing bags whizzing along miles of subterranean conveyor belts before tipping into baggage chutes. He shows us a map of the belts that looks like tangled spaghetti. We visit a thunderous cavern to watch bags descending an extraordinary helter-skelter that takes them 60 metres down into the bowels of Terminal 1, and from there along a mile-long tunnel to Terminal 4. It is a “stone-age” system, he concedes.

The airlines’ responsibility is to load and unload the bags from planes. Wazacz claims that 55 per cent of bags miss their connecting flights because of delays getting them on or off aircraft. He says the airlines have an informal agreement with BAA to unload all bags within 25 minutes of landing, but the three British carriers – Virgin, BMi and BA – achieved that only 78, 66 and 34 per cent of the time in June. He will not say which is the worst of the three, but it is obviously BA whose baggage-handling operation is undermanned and heavily unionised, and whose record this summer has been lamentable. It has lost one bag for every 36 passengers. It was recently forced to truck thousands of mislaid bags from Heathrow to Milan to sort them out, and came bottom of an industry league table.

From the antiquated depths of Terminal 1 we soar to the ultra-modern heights of Heathrow’s new control tower, twice as tall as Nelson’s column, where we watch plane after plane coming in over London to land, each 2.5 miles and 90 seconds apart. More than 40 land each hour. A similar number take off on the parallel runway. Heathrow’s two runways are used to 98.5 per cent of their capacity, which is why one small glitch – bad weather, a security scare – can cause disproportionate chaos.

Leaving the tower we meet Shaun Cowlam, Heathrow’s logistics director. He was a brigadier who ran the British Army’s logistics operation during the 2003 invasion of Iraq, and says the scale and complexity of running Heathrow is very similar. We challenge him on other perceived shortcomings of the airport – broken escalators, trolleys that won’t push straight, filthy lavatories.

He says that by the year’s end he will have introduced 14,000 new trolleys equipped with Radio Frequency ID tags so they can be tracked and taken where needed. He says he has permanently manned each of Heathrow’s main lavatories to “try to introduce pride in ownership”, but complains that the toilets are sometimes blocked by asylum-seekers flushing away their passports.

Cowlam, 50, laments Heathrow’s relentless bad publicity. “I worry that our workforce is constantly at the bitter end of some of the comment and observations,” he says. “They know that much of what’s said is factually incorrect and doesn’t represent the truth. It’s not as bleak as it is made out in the press.”

A visit to the airport’s nearly-completed Terminal 5 is mandatory, of course, for that is BAA’s remedy for Heathrow’s fundamental problem: it presently funnels 67 million passengers a year through geriatric facilities designed for 45 million.

We are escorted by Mike Forster, 53, BAA’s head of strategy, who is enormously proud of a project he has nurtured for ten years. The £4.3 billion terminal, designed by Richard Rogers and opening in March, is indeed magnificent – vast, bright and airy, with Britain’s largest single-span roof, enough floor space for 50 football pitches, a six-platform railway station and much else besides. Forster angrily rebutts recent reports that it will have just 700 seats to allow maximum space for BAA’s money-spinning shops. It will have 9,000, he insists.

Terminal 5 will absorb 30 million passengers a year, permitting the redevelopment of the rest of Heathrow. Work has already started on Terminal 3’s forecourt, Terminal 4’s refurbishment will begin when BA moves into Terminal 5, and phase one of a £1.5 billion terminal called Heathrow East is intended to replace Terminals 1 and 2 in time for the 2012 London Olympics.

Forster says he feels a “passion” for transforming Heathrow. “We know Heathrow should be better and we have a plan to make it better. Our belief is that by the time we have worked it through Heathrow will be a place the UK will be proud of rather than fed up with.” The condition, of course, is that the Civil Aviation Authority, which is presently reviewing BAA’s tariffs for the next five years, allows it to double landing charges to pay for its £6.2 billion investment programme. That is why BAA is so eager to blame others for Heathrow’s present shortcomings – and why the airlines have a vested interest in denigrating BAA. The stakes are huge.

At 7.30pm Ward is alone in his office, still working and still full of figures that defy popular perceptions: 76 per cent of flights leave Heathrow within 15 minutes of their scheduled departure times, and 23 per cent within an hour. Another text pings up on his mobile. It says that the only security queues that had exceeded ten minutes that day involved transfer passengers, that there had been two emergency landings (neither serious), and that the protest camp had caused no problems.

The 300 bags were still sitting in the reclaim hall, but Ward was content. “It’s not perfect, but it’s a world apart from what it was a year ago.” The travelling public may or may not agree.